package com.example.sequences.core.jpa;

import org.apache.commons.lang3.StringUtils;

/**
 * IdGenerator
 *
 * @author maxsc
 * @title IdGenerator.java
 * @date 2018/5/8
 */
public class IdGenerator {
    private final long workerId;
    private final static long twepoch = 1361753741828L;
    private long sequence = 0L;
    private final static long workerIdBits = 4L;
    public final static long maxWorkerId = -1L ^ -1L << workerIdBits;
    private final static long sequenceBits = 10L;
    private final static long workerIdShift = sequenceBits;
    private final static long timestampLeftShift = sequenceBits + workerIdBits;
    public final static long sequenceMask = -1L ^ -1L << sequenceBits;

    private long lastTimestamp = -1L;

    public static IdGenerator getInstance() {
        return IdWorkHolder.INSTANCE;
    }

    private static class IdWorkHolder {
        public static final IdGenerator INSTANCE = new IdGenerator(1);
    }

    private IdGenerator(final long workerId) {
        super();
        if (workerId > this.maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format(
                    "worker Id can't be greater than %d or less than 0",
                    this.maxWorkerId));
        }
        this.workerId = workerId;
    }

    public synchronized String nextId(String modelMark) {
        if (StringUtils.isEmpty(modelMark)) {
            throw new RuntimeException(" the model mark is not exist! ");
        }
        if(modelMark.length() > 7 ){
            throw new RuntimeException(" the model mark is too long ! ");
        }

        return modelMark + Long.toHexString(nextSequence()).toUpperCase();
    }

    private long nextSequence() {
        long timestamp = this.timeGen();
        if (this.lastTimestamp == timestamp) {
            this.sequence = (this.sequence + 1) & this.sequenceMask;
            if (this.sequence == 0) {
                System.out.println("###########" + sequenceMask);
                timestamp = this.tilNextMillis(this.lastTimestamp);
            }
        } else {
            this.sequence = 0;
        }

        if (timestamp < this.lastTimestamp) {
            try {
                throw new Exception(
                        String.format( "Clock moved backwards.  Refusing to generate id for %d milliseconds",
                                this.lastTimestamp - timestamp));
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        this.lastTimestamp = timestamp;
        long nextId = ((timestamp - twepoch << timestampLeftShift)) | (this.workerId << this.workerIdShift) | (this
                .sequence);
        return nextId;
    }

    private long tilNextMillis(final long lastTimestamp) {
        long timestamp = this.timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = this.timeGen();
        }
        return timestamp;
    }

    private long timeGen() {
        return System.currentTimeMillis();
    }
}
